(a) Field of the Invention
The present invention relates to a helical antenna manufacturing apparatus and method. More specifically, the present invention relates to a helical antenna, and an apparatus and method for automatically manufacturing the helical antenna.
(b) Description of the Related Art
Helical antennas are widely used in mobile stations. A helical antenna is an antenna in which copper lines are helically wound on a core made of an insulative material, thereby enabling the size of the antenna to be reduced. The performance of the helical antenna greatly affects the performance of the mobile station.
Referring to drawings, the prior helical antennas will now be described.
FIGS. 1(a) and (b) show schematic views of prior helical antennas used in conventional mobile stations.
As shown in FIG. 1(a), the conventional helical antenna is formed such that copper lines 2 are helically wound on a plastic core 1, that is, an insulative core. A conductive feeder 3, which is electrically connected to an external circuit, is formed on the lower part of the plastic core 1. An outer surface of the plastic core 1 is sealed with plastic resin 4.
This conventional antenna is manufactured using the following method. Referring to FIG. 1(a), grooves are helically formed on the outer surface of the cylindrical plastic core 1, and the copper lines 2 of a length of xcex/4 are wound on the core 1 to form a helical line. Next, the conductive feeder 3, which is a fixed metallic body, is attached to the lower part of the plastic core 1, and the outer surface of the core 1 is molded with the plastic resin 4 by an injection molding process, thereby completing the manufacture of the helical antenna.
The characteristics of such a helical antenna depend on the helical lines, that is, the total length of the copper lines, pitch gaps between the copper lines, and a diameter of the core. Therefore, such dimensions must be carefully designed in order to enable the helical antenna to be operated in a desired frequency band.
However, in the case where the helical antenna is manufactured as described above (i.e., winding the copper lines on the plastic core), since the radio frequency (RF) characteristics of the plastic is low, the frequency characteristics of the antenna itself become lower. Also, the injection and molding processes required to manufacture the grooved plastic core have drawbacks in that they are accompanied by a high defective rate. These processes also make mass production difficult.
Hence, a helical antenna has been developed in which a core is not used. FIG. 1(b) shows a prior helical antenna in which no core is used.
As shown in FIG. 1(b), the helical antenna includes a spiral coil 5, a feeder 3 formed on the lower end of the coil 5, and plastic resin 4 formed as a seal surrounding the coil 5.
When manufacturing this helical antenna, an operator cuts the coil 5 to a predetermined length, attaches the feeder 3 to the lower end of the cut coil 5, and molds the outer surface of the coil 5 with the plastic resin 4 to complete the manufacture of the helical antenna.
There are at present various wireless communications services such as Code Division Multiple Access (CDMA), Personal Communication Service (PCS), Global System for Mobile communication (GSM), and Digital European Cordless Telephone (DECT), each using different frequency bands. Because of the different frequency bands used and the general incompatibility of these wireless communications services, it has become necessary to design multi-band antennas which enable use in various frequency bands. FIGS. 2(a) and (b) show schematic views of additional conventional helical antennas used in prior mobile stations.
As shown in FIG. 2(a), two copper lines 2 having differently designed resonance frequencies are formed on the plastic core 1, which is made of insulative material. As shown in FIG. 2(b), the helical antenna can also be manufactured with a spiral coil 5 and no use of a core. By making the number of spirals and the pitches of an upper coil 5a differently from those of a lower coil 5b, a helical antenna which operates in different resonance frequency bands can be manufactured.
As the frequencies used in mobile stations become higher, helical antennas with a high degree of precision are needed. However, in the case of manufacturing helical antennas by the conventional methods, since the operator manually cuts the coil to a predetermined length according to the operative frequency bands, productivity is limited and the precision is reduced. Further, in the case where a coil is used without a core, since the coil is deformed because of the elasticity of the coil itself, a surface molding process cannot be performed. Instead, a cover made of resin is placed on the coil to protect the coil. Consequently, the adhesive strength between the metallic feeder and the coil can be weakened such that the smooth operation of the antenna is at times unable to be realized. Also, in the conventional antenna where a core is used, because the resin is injected at a high pressure during the molding process, collision with the coil results so that the coil is deformed. This may act to change the resonance frequencies of the antenna, thereby decreasing productivity.
Further, since the resonance frequencies can be changed by different tensions in the coil, the operator must manually tune all the antennas. For this and other reasons, it is difficult to automate the conventional helical antenna manufacturing process. This results in a low rate of productivity, ultimately increasing manufacturing costs. In addition to these problems, since this conventional helical antenna is installed on an upper part of the communication device and protruded therefrom, that is, because of the external mounting of the antenna, the helical antenna can be damaged by receiving shock when the device is dropped, etc. Also, such a configuration makes the communication device difficult to handle. To overcome these problems, helical antennas which can be built within the communication device are being developed, and one such helical antenna is the micro-strip patch antenna. However, since the radiator of the conventional built-in antennas must be xcex/2 in size, the whole size of the antenna becomes very big. To increase the usable bandwidth of the microstrip antenna, the width of the radiator and the thickness of a substrate must be increased, and therefore, the whole volume and weight of the antenna is increased. Hence, such built-in antennas are not suitable for use as helical antennas for mobile stations.
Since radiation occurs only in the direction of the upper part of the substrate on which the radiator is formed and not toward the lower part of the substrate on which ground patterns are formed in the conventional built-in antenna, the antenna develops directional properties. As a result, the sensitivity of the antenna is varied according to the direction the antenna is pointed.
It is important to note here that it is not feasible to install the helical antenna of FIGS. 1 and 2 within the mobile station since this would make it difficult to make the mobile station small in size. That is, since the antenna is formed by winding the copper lines on the plastic core or by using a spring-type coil, the copper lines or the coil can be deformed when the mobile station receives external shock. Accordingly, the antenna must be molded or sealed with a cover in order to prevent such deformation, which increases the entire size of the mobile station. Also, an additional metallic fixture is needed for connection with a print circuit board (PCB) of the mobile station, again acting to increase the size of the mobile station. Further, because of the difficulties in providing the antenna in a surface-mounted configuration, it is nearly impossible to install the antenna within the communication device.
Since a planar inverted F antenna (PIFA) is also big in size, the PIFA cannot be applied to a small device such as a wireless LAN card. The PIFA also has directional problems. In some cases, the antenna is manufactured as a chip and equipped within the device. However, such a chip-type antenna has low antenna characteristics, and therefore, can only be used in such devices as cordless phones.
It is an object of the present invention to provide an apparatus and method for automatically manufacturing helical antennas.
In one aspect of the present invention, a helical antenna manufacturing apparatus comprises a core made of insulative material; a first roller printing a conductive and viscous paste on a surface of the core to form a helical line; a roller driver rotating the first roller; a core driver rotating the core and moving the same in a longitudinal direction; and a controller controlling the roller driver and the core driver to control an rpm of the core, a longitudinal moving speed of the core, and the rpm of the roller, the longitudinal moving speed being set according to working frequency bands of the antenna.
The apparatus further comprises a paste box containing the paste; and a paste provider comprising a paste injector injecting the paste into the paste box.
The apparatus further comprises one or more second rollers contacted to the paste in the paste box and rotated, and providing the paste to the first roller.
An outer circumference of the first roller is sloped at a predetermined angle.
A diameter of a central part of the first roller is greater than a diameter of an outer part of the first roller.
The apparatus further comprises a core provider providing the core to a position to be contacted with the first roller; and a drier drying the core on which the helical line is formed.
In another aspect of the present invention, a helical antenna manufacturing apparatus comprises a core made of insulative material; a roller printing a conductive and viscous paste on a surface of the core to form a helical line unit comprising a first helical line of a first frequency band and a second helical line of a second frequency band; a roller driver rotating the roller; a core driver rotating the core and moving the same in a longitudinal direction of the core; and a controller controlling the roller driver and the core driver to control an rpm of the core and an rpm of the roller, and sequentially controlling the core driver according to a first moving speed which is set according to the first frequency band at which the antenna is operated and according to a second moving speed which is set according to the second frequency band.
In a further aspect of the present invention, a helical antenna manufacturing method comprises the steps of printing a conductive helical line on a surface of a core made of insulative material; dipping a part of the core in a conductive paste to form a terminal; connecting a feeder to the terminal of the core, the feeder being electrically connected to an external circuit; and sealing an outer part of the core with a cover of insulative material.